Memory Array Test Structure and Method of Forming the Same

ABSTRACT

A test structure for 3D memory arrays and methods of forming the same are disclosed. In an embodiment, a memory array includes a first word line over a semiconductor substrate and extending in a first direction; a second word line over the first word line and extending in the first direction; a memory film contacting the first word line and the second word line; an oxide semiconductor (OS) layer contacting a first source line and a first bit line, the memory film being between the OS layer and each of the first word line and the second word line; and a test structure over the first word line and the second word line, the test structure including a first conductive line electrically coupling the first word line to the second word line, the first conductive line extending in the first direction.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional of U.S. patent application Ser. No.17/397,414, filed on Aug. 9, 2021, which claims the benefit of U.S.Provisional Application No. 63/211,765, filed on Jun. 17, 2021, whichapplications are hereby incorporated herein by reference.

BACKGROUND

Semiconductor memories are used in integrated circuits for electronicapplications, including radios, televisions, cell phones, and personalcomputing devices, as examples. Semiconductor memories include two majorcategories. One is volatile memories; the other is non-volatilememories. Volatile memories include random access memory (RAM), whichcan be further divided into two sub-categories, static random accessmemory (SRAM) and dynamic random access memory (DRAM). Both SRAM andDRAM are volatile because they will lose the information they store whenthey are not powered.

On the other hand, non-volatile memories can keep data stored on them.One type of non-volatile semiconductor memory is ferroelectric randomaccess memory (FERAM, or FRAM). Advantages of FERAM include its fastwrite/read speed and small size.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A and 1B illustrate a perspective view and a circuit diagram of amemory array in accordance with some embodiments.

FIGS. 2, 3, 4, 5, 6, 7, 8, 9, 10, 11A, 11B, 11C, 12A, 12B, 12C, 13A,13B, 13C, 14A, 14B, 14C, 15A, 15B, 15C, 16A, 16B, 16C, 17A, 17B, 17C,18A, 18B, 18C, 19A, 19B, 19C, 20A, 20B, 20C, 20D, 21A, 21B, 21C, 21D,22A, 22B, 22C, 23A, 23B, 23C, 24A, 24B, 24C, 24D, 25A, 25B, 25C, 26A,26B, 27A, 27B, 28A, 28B, 29A, 29B, 30A, 30B, 31A, 31B, 32A, 32B, 33A,33B, 34A, 34B, and 34C illustrate varying views of manufacturing asemiconductor device including a memory array in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Various embodiments provide a test structure for testing connectionswithin a staircase structure for a 3D memory array and a method offorming the same. The 3D memory array includes stacked memory cells,which include word lines extending in a direction parallel to a majorsurface of an underlying substrate. The word lines are arranged in astaircase structure with respective lengths of the word lines decreasingin a direction away from the substrate. An inter-metal dielectric (IMD)may be formed over the staircase structure and conductive vias may beformed through the IMD and extending to each of the word lines in thestaircase structure. The conductive vias may be formed simultaneouslyusing a single mask, which saves time and cost, but may carry a risk ofopenings for the conductive vias not extending to sufficient depths. Assuch, a test structure may be formed over the staircase structure totest whether each of the conductive vias has been successfully connectedto a respective word line. The test structure includes conductive linesconnected to each of the conductive vias, and which interconnect each ofthe word lines in the staircase structure. Some of the conductive linesextend in a direction parallel to the word lines, and some of theconductive lines extend in a direction perpendicular to the word lines.A voltage bias may be applied to opposite ends of the test structure,through all of the word lines, in order to determine whether all of theconductive vias are successfully connected to the respective word lines.The test structure may be used to screen memory arrays in whichconductive vias are not successfully connected to respective word lines,which reduces device defects.

FIGS. 1A and 1B illustrate examples of a memory array 200, according tosome embodiments. FIG. 1A illustrates an example of a portion of thememory array 200 in a three-dimensional view. FIG. 1B illustrates acircuit diagram of the memory array 200. The memory array 200 includes aplurality of memory cells 202, which may be arranged in a grid of rowsand columns. The memory cells 202 may be further stacked vertically toprovide a three-dimensional memory array, thereby increasing devicedensity. The memory array 200 may be disposed in the back end of line(BEOL) of a semiconductor die. For example, the memory array 200 may bedisposed in the interconnect layers of the semiconductor die, such asabove one or more active devices (e.g., transistors) formed on asemiconductor substrate.

In some embodiments, the memory array 200 is a flash memory array, suchas an NOR flash memory array or the like. Each of the memory cells 202may include a transistor 204 with memory films 90. The memory films 90may serve as gate dielectrics. In some embodiments, a gate of eachtransistor 204 is electrically coupled to a respective word line (e.g.,a conductive line 72), a first source/drain region of each transistor204 is electrically coupled to a respective bit line (e.g., a conductiveline 106), and a second source/drain region of each transistor 204 iselectrically coupled to a respective source line (e.g., a conductiveline 108), which electrically couples the second source/drain region toground. The memory cells 202 in a same horizontal row of the memoryarray 200 may share a common word line, while the memory cells 202 in asame vertical column of the memory array 200 may share a common sourceline and a common bit line.

The memory array 200 includes a plurality of vertically stackedconductive lines 72 (e.g., word lines) with first material layers 52disposed between vertically adjacent ones of the conductive lines 72.The conductive lines 72 extend in a direction parallel to a majorsurface of an underlying substrate (not separately illustrated in FIGS.1A and 1B). The conductive lines 72 may have a staircase configurationsuch that lower conductive lines 72 are longer than and extendlongitudinally past endpoints of upper conductive lines 72. For example,in FIG. 1A, multiple, stacked layers of conductive lines 72 areillustrated with topmost conductive lines 72 being the shortest andbottommost conductive lines 72 being the longest. Respective lengths ofthe conductive lines 72 may increase in a direction towards theunderlying substrate. In this manner, a portion of each of theconductive lines 72 may be accessible from above the memory array 200,and conductive contacts may be made to an exposed portion of each of theconductive lines 72.

The memory array 200 further includes a plurality of conductive lines106 (e.g., bit lines) and a plurality of conductive lines 108 (e.g.,source lines). The conductive lines 106 and the conductive lines 108 mayeach extend in a direction perpendicular to the conductive lines 72.Dielectric materials 102 are disposed between and isolate adjacent onesof the conductive lines 106 and the conductive lines 108. Pairs of theconductive lines 106 and the conductive lines 108 along with anintersecting conductive line 72 define boundaries of each memory cell202, and dielectric materials 98 are disposed between and isolateadjacent pairs of the conductive lines 106 and the conductive lines 108.In some embodiments, the conductive lines 108 are electrically coupledto ground. Although FIG. 1A illustrates a particular placement of theconductive lines 106 relative to the conductive lines 108, it should beappreciated that the placement of the conductive lines 106 and theconductive lines 108 may be flipped.

The memory array 200 may also include oxide semiconductor (OS) layers92. The OS layers 92 may provide channel regions for the transistors 204of the memory cells 202. For example, when an appropriate voltage (e.g.,higher than a respective threshold voltage (Vth) of a correspondingtransistor 204) is applied through a corresponding conductive line 72, aregion of the OS layers 92 that intersects the conductive line 72 mayallow current to flow from the conductive lines 106 to the conductivelines 108 (e.g., in the direction indicated by arrow 206).

The memory films 90 are disposed between the conductive lines 72 and theOS layers 92, and the memory films 90 may provide gate dielectrics forthe transistors 204. In some embodiments, the memory films 90 compriseferroelectric (FE) materials, such as hafnium oxide, hafnium zirconiumoxide, silicon-doped hafnium oxide, or the like. Accordingly, the memoryarray 200 may be referred to as a ferroelectric random access memory(FERAM) array. Alternatively, the memory films 90 may be multilayerstructures, different ferroelectric materials, different types of memorylayers (e.g., capable of storing a bit), or the like.

In embodiments in which the memory films 90 comprise FE materials, thememory films 90 may be polarized in one of two different directions. Thepolarization direction may be changed by applying an appropriate voltagedifferential across the memory films 90 and generating an appropriateelectric field. The polarization may be relatively localized (e.g.,generally contained within each boundaries of the memory cells 202) andcontinuous regions of the memory films 90 may extend across a pluralityof memory cells 202. Depending on a polarization direction of aparticular region of the memory films 90, a threshold voltage of acorresponding transistor 204 varies and a digital value (e.g., a 0 ora 1) can be stored. For example, when a region of the memory films 90has a first electrical polarization direction, the correspondingtransistor 204 may have a relatively low threshold voltage, and when theregion of the memory films 90 has a second electrical polarizationdirection, the corresponding transistor 204 may have a relatively highthreshold voltage. The difference between the two threshold voltages maybe referred to as the threshold voltage shift. A larger thresholdvoltage shift makes it easier (e.g., less error prone) to read thedigital value stored in the corresponding memory cell 202.

To perform a write operation on a memory cell 202, a write voltage isapplied across a portion of the memory films 90 corresponding to thememory cell 202. The write voltage can be applied, for example, byapplying appropriate voltages to a corresponding conductive line 72(e.g., a corresponding word line) and the corresponding conductive lines106 and conductive lines 108 (e.g., corresponding bit and source lines).By applying the write voltage across the portion of the memory films 90,a polarization direction of the region of the memory films 90 can bechanged. As a result, the corresponding threshold voltage of thecorresponding transistor 204 can be switched from a low thresholdvoltage to a high threshold voltage or vice versa and a digital valuecan be stored in the memory cell 202. Because the conductive lines 72intersect the conductive lines 106 and the conductive lines 108,individual memory cells 202 may be selected for the write operation.

To perform a read operation on the memory cell 202, a read voltage(e.g., a voltage between the low and high threshold voltages) is appliedto the corresponding conductive line 72 (e.g., the corresponding wordline). Depending on the polarization direction of the correspondingregion of the memory films 90, the transistor 204 of the memory cell 202may or may not be turned on. As a result, the corresponding conductiveline 106 may or may not be discharged through the correspondingconductive line 108 (e.g., the corresponding source line that is coupledto ground), and the digital value stored in the memory cell 202 can bedetermined. Because the conductive lines 72 intersect the conductivelines 106 and the conductive lines 108, individual memory cells 202 maybe selected for the read operation.

FIG. 1A further illustrates reference cross-sections of the memory array200 that are used in later figures. Cross-section A-A′ is alonglongitudinal axes of conductive lines 72 and in a direction, forexample, parallel to the direction of current flow across the OS layers92 of the transistors 204. Cross-section B-B′ is perpendicular to thecross-section A-A′ and the longitudinal axes of the conductive lines 72.The cross-section B-B′ extends through the dielectric materials 98 andthe dielectric materials 102. Cross-section C-C′ is parallel to thecross-section B-B′ and extends through the conductive lines 106.Subsequent figures refer to these reference cross-sections for clarity.Cross-section D-D′ is parallel to the cross-section B-B′ and extendsthrough a staircase structure portion of the conductive lines 72.

FIGS. 2 through 34C are views of intermediate stages in themanufacturing of the memory array 200, in accordance with someembodiments. FIGS. 2, 3, 4, 5, 6, 7, 8, 9, 10, 11B, 12B, 13B, 14B, 15B,16B, 17B, 18B, 19B, 20B, 21B, 22B, 23B, and 24B are illustrated alongreference cross-section A-A′ illustrated in FIG. 1A. FIGS. 11C, 12C,13C, 14C, 15C, 16C, 17C, 18C, 19C, 20C, 21C, 26A, 27A, 28A, 29A, 30A,31A, 32A, 33A, and 34A are illustrated along reference cross-sectionB-B′ illustrated in FIG. 1A. FIGS. 20D, 21D, and 34C are illustratedalong reference cross-section C-C′ illustrated in FIG. 1A. FIGS. 22C,23C, 24C, 26B, 27B, 28B, 29B, 30B, 31B, 32B, 33B, and 34B areillustrated along reference cross-section D-D′ illustrated in FIG. 1A.FIGS. 11A, 12A, 13A, 14A, 15A, 16A, 17A, 18A, 19A, 20A, 21A, 22A, 23A,24A, 25A, and 25C illustrate top-down views. FIGS. 24D, 25B illustrateperspective views.

In FIG. 2 , a substrate 50 is provided. The substrate 50 may be asemiconductor substrate, such as a bulk semiconductor, asemiconductor-on-insulator (SOI) substrate, or the like, which may bedoped (e.g., with a p-type or an n-type dopant) or undoped. Thesubstrate 50 may be an integrated circuit die, such as a logic die, amemory die, an ASIC die, or the like. The substrate 50 may be acomplementary metal oxide semiconductor (CMOS) die and may be referredto as a CMOS under array (CUA). The substrate 50 may be a wafer, such asa silicon wafer. Generally, an SOI substrate is a layer of asemiconductor material formed on an insulator layer. The insulator layermay be, for example, a buried oxide (BOX) layer, a silicon oxide layer,or the like. The insulator layer is provided on a substrate, typically asilicon or a glass substrate. Other substrates, such as multi-layered orgradient substrates may also be used. In some embodiments, thesemiconductor material of the substrate 50 may include silicon;germanium; a compound semiconductor including silicon carbide, galliumarsenide, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; an alloy semiconductor including silicon-germanium,gallium arsenide phosphide, aluminum indium arsenide, aluminum galliumarsenide, gallium indium arsenide, gallium indium phosphide, and/orgallium indium arsenide phosphide; or combinations thereof.

FIG. 2 further illustrates circuits that may be formed over thesubstrate 50. The circuits include transistors at a top surface of thesubstrate 50. The transistors may include gate dielectric layers 302over top surfaces of the substrate 50 and gate electrodes 304 over thegate dielectric layers 302. Source/drain regions 306 are disposed in thesubstrate 50 on opposite sides of the gate dielectric layers 302 and thegate electrodes 304. Gate spacers 308 are formed along sidewalls of thegate dielectric layers 302 and separate the source/drain regions 306from the gate electrodes 304 by appropriate lateral distances. Thetransistors may comprise fin field effect transistors (FinFETs),nanostructure (e.g., nanosheet, nanowire, gate-all-around, or the like)FETS (nano-FETs), planar FETs, the like, or combinations thereof, andmay be formed by gate-first processes or gate-last processes.

A first ILD 310 surrounds and isolates the source/drain regions 306, thegate dielectric layers 302, and the gate electrodes 304 and a second ILD312 is over the first ILD 310. Source/drain contacts 314 extend throughthe second ILD 312 and the first ILD 310 and are electrically coupled tothe source/drain regions 306. Gate contacts 316 extend through thesecond ILD 312 and are electrically coupled to the gate electrodes 304.An interconnect structure 320 including one or more stacked dielectriclayers 324 and conductive features 322 formed in the one or moredielectric layers 324 is over the second ILD 312, the source/draincontacts 314, and the gate contacts 316. The interconnect structure 320may be electrically connected to the gate contacts 316 and thesource/drain contacts 314 to form functional circuits. In someembodiments, the functional circuits formed by the interconnectstructure 320 may comprise logic circuits, memory circuits, senseamplifiers, controllers, input/output circuits, image sensor circuits,the like, or combinations thereof. Although FIG. 2 discusses transistorsformed over the substrate 50, other active devices (e.g., diodes or thelike) and/or passive devices (e.g., capacitors, resistors, or the like)may also be formed as part of the functional circuits. The transistors,the ILDs, and the interconnect structure 320 formed over the substrate50 may be omitted from subsequent drawings for the purposes ofsimplicity and clarity. The substrate 50 along with the transistors(e.g., the source/drain regions 306, the gate dielectric layers 302, andthe gate electrodes 304), the gate spacers 308, the first ILD 310, thesecond ILD 312, and the interconnect structure 320 may be a CMOS underarray (CUA), a logic die, or the like.

In FIG. 3 , a multi-layer stack 58 is formed over the substrate 50.Although the multi-layer stack 58 is illustrated as contacting thesubstrate 50, any number of intermediate layers may be disposed betweenthe substrate 50 and the multi-layer stack 58. For example, one or moreinterconnect layers comprising conductive features in insulting layers(e.g., low-k dielectric layers) may be disposed between the substrate 50and the multi-layer stack 58. In some embodiments, the conductivefeatures may be patterned to provide power, ground, and/or signal linesfor the active devices on the substrate 50 and/or the memory array 200(see FIGS. 1A and 1B).

The multi-layer stack 58 includes alternating layers of first materiallayers 52A-52D (collectively referred to as first material layers 52)and second material layers 54A-54C (collectively referred to as secondmaterial layers 54). In some embodiments, the second material layers 54may be patterned in subsequent steps to define conductive lines 72(e.g., word lines). In embodiments in which the second material layers54 are patterned to define the conductive lines 72, the second materiallayers 54 may comprise conductive materials, such as, copper, titanium,titanium nitride, tantalum, tantalum nitride, tungsten, ruthenium,aluminum, cobalt, silver, gold, nickel, chromium, hafnium, platinum,combinations thereof, or the like. The first material layers 52 maycomprise insulating materials, such as silicon oxide, silicon nitride,silicon oxynitride, combinations thereof, or the like. In someembodiments, the second material layers 54 may be replaced in subsequentsteps by conductive materials, which define the conductive lines 72. Insuch embodiments, the second material layers 54 may also compriseinsulating materials, such as silicon oxide, silicon nitride, siliconoxynitride, combinations thereof, or the like, and may include materialshaving a high etch selectivity to materials of the first material layers52. In some embodiments, the first material layers 52 may comprise anoxide, such as silicon oxide, and the second material layers 54 maycomprise a nitride, such as silicon nitride. The first material layers52 and the second material layers 54 may each be formed using, forexample, CVD, ALD, physical vapor deposition (PVD), plasma enhanced CVD(PECVD), or the like. Although FIG. 3 illustrates a particular number ofthe first material layers 52 (e.g., 4) and the second material layers 54(e.g., 3), other embodiments may include different numbers of the firstmaterial layers 52 and the second material layers 54.

FIGS. 4 through 8 illustrate patterning the multi-layer stack 58 to forma staircase structure 68 (illustrated in FIG. 8 ). In FIG. 4 , aphotoresist 56 is formed over the multi-layer stack 58. The photoresist56 can be formed by using a spin-on technique and can be patterned usingacceptable photolithography techniques. Patterning the photoresist 56may expose the multi-layer stack 58 in a region 60, while maskingremaining portions of the multi-layer stack 58. For example, a topmostlayer of the multi-layer stack 58 (e.g., the first material layer 52D)may be exposed in the region 60.

In FIG. 5 , the exposed portions of the multi-layer stack 58 in theregion 60 are etched using the photoresist 56 as a mask. The etching maybe any acceptable etch process, such as wet or dry etching, reactive ionetching (RIE), neutral beam etching (NBE), the like, or a combinationthereof. The etching may be anisotropic. The etching may remove portionsof the first material layer 52D and the second material layer 54C in theregion 60 and define openings 61 along opposite edges of the multi-layerstack 58. Because the first material layers 52 and the second materiallayers 54 have different material compositions, etchants used to removeexposed portions of these layers may be different. In some embodiments,the second material layer 54C acts as an etch stop layer while etchingthe first material layer 52D, and the first material layer 52C acts asan etch stop layer while etching the second material layer 54C. As aresult, the portions of the first material layer 52D and the secondmaterial layer 54C may be selectively removed without removing remaininglayers of the multi-layer stack 58, and the openings 61 may be extendedto desired depths. Alternatively, a timed etch processes may be used tostop the etching of the openings 61 after the openings 61 reach thedesired depths. In the resulting structure, the first material layer 52Cis exposed in the region 60.

In FIG. 6 , the photoresist 56 is trimmed to expose additional portionsof the multi-layer stack 58. The photoresist 56 can be trimmed usingacceptable photolithography techniques. As a result of the trimming, awidth of the photoresist 56 is reduced, and portions the multi-layerstack 58 in the region 60 and a region 62 are exposed. For example, topsurfaces of the first material layer 52D in the region 62 and topsurfaces of the first material layer 52C in the region 60 may beexposed.

Exposed portions of the multi-layer stack 58 may then be etched usingthe photoresist 56 as a mask. The etching may be any suitable etchingprocess, such as wet or dry etching, RIE, NBE, the like, or acombination thereof. The etching process may be anisotropic. The etchingmay extend the openings 61 further into the multi-layer stack 58.Because the first material layers 52 and the second material layers 54have different material compositions, etchants used to remove exposedportions of these layers may be different. In some embodiments, thesecond material layers 54 act as etch stop layers while etching thefirst material layers 52, and the first material layers 52 act as etchstop layers while etching the second material layers 54. As a result,the portions of the first material layers 52 and the second materiallayers 54 may be selectively removed without removing remaining layersof the multi-layer stack 58, and the openings 61 may be extended todesired depths. Alternatively, timed etch processes may be used to stopthe etching of the openings 61 after the openings 61 reach the desireddepths. Further, during the etching process, un-etched portions of thefirst material layers 52 and the second material layers 54 act as masksfor underlying layers, and as a result a previous pattern of the firstmaterial layer 52D and the second material layer 54C (see FIG. 5 ) maybe transferred to the underlying first material layer 52C and theunderlying second material layer 54B. In the resulting structure, thefirst material layer 52C is exposed in the region 62 and the firstmaterial layer 52B is exposed in the region 60.

In FIG. 7 , the photoresist 56 is trimmed to expose additional portionsof the multi-layer stack 58. The photoresist 56 can be trimmed usingacceptable photolithography techniques. As a result of the trimming, awidth of the photoresist 56 is reduced, and portions the multi-layerstack 58 in the region 60, the region 62, and a region 64 are exposed.For example, top surfaces of the first material layer 52D in the region64, top surfaces of the first material layer 52C in the region 62, andtop surfaces of the first material layer 52B in the region 60 may beexposed.

Exposed portions of the multi-layer stack 58 may then be etched usingthe photoresist 56 as a mask. The etching may be any suitable etchingprocess, such as wet or dry etching, RIE, NBE, the like, or acombination thereof. The etching process may be anisotropic. The etchingmay extend the openings 61 further into the multi-layer stack 58. Thesecond material layers 54 may act as etch stop layers while etching thefirst material layers 52. As a result, the portions of the firstmaterial layers 52 may be selectively removed without removingunderlying portions of the second material layers 54, and the openings61 may be extended to desired depths. Alternatively, timed etchprocesses may be used to stop the etching of the openings 61 after theopenings 61 reach the desired depths. Further, during the etchingprocess, un-etched portions of the first material layers 52 and thesecond material layers 54 act as masks for underlying layers, and as aresult a previous pattern of the first material layer 52D, the secondmaterial layer 54C, the first material layer 52C, and the secondmaterial layer 54B (see FIG. 6 ) may be transferred to the underlyingfirst material layer 52B and the underlying first material layer 52C. Inthe resulting structure, the second material layer 54C is exposed in theregion 64, the second material layer 54B is exposed in the region 62 andthe second material layer 54A is exposed in the region 60.

In FIG. 8 the photoresist 56 is removed. The photoresist 56 may beremoved by an acceptable ashing or wet strip process. Thus, a staircasestructure 68 is formed. The staircase structure 68 comprises a stack ofalternating layers of the first material layers 52 and the secondmaterial layers 54. As illustrated in FIG. 8 , forming the staircasestructure 68 allows for portions of each of the second material layers54A-54C to be exposed from overlying second material layers 54 and firstmaterial layers 52. As a result, conductive contacts can be made fromabove the staircase structure 68 to each of the second material layers54 in subsequent processing steps.

In FIG. 9 , an inter-metal dielectric (IMD) 70 is deposited over themulti-layer stack 58. The IMD 70 may be formed of a dielectric material,and may be deposited by any suitable method, such as CVD, PECVD,flowable CVD (FCVD), or the like. The dielectric materials may includephospho-silicate glass (PSG), boro-silicate glass (BSG), boron-dopedphospho-silicate glass (BPSG), undoped silicate glass (USG), or thelike. In some embodiments, the IMD 70 may comprise an oxide (e.g.,silicon oxide or the like), a nitride (e.g., silicon nitride or thelike), a combination thereof or the like. Other dielectric materialsformed by any acceptable process may be used. The IMD 70 extends alongsidewalls of the first material layers 52B-52D, sidewalls of the secondmaterial layers 54B and 54C, a top surface of the first material layer52D, and top surfaces of the second material layers 54A-54C.

In FIG. 10 , a removal process is applied to the IMD 70 to remove excessdielectric material over the multi-layer stack 58. In some embodiments,the removal process may be a planarization process, such as a chemicalmechanical polish (CMP), an etch-back process, combinations thereof, orthe like. The planarization process exposes the multi-layer stack 58such that top surfaces of the first material layer 52D and the IMD 70are level after the planarization process is complete.

In FIGS. 11A through 13C, trenches 86 (illustrated in FIGS. 12A through13C) are formed in the multi-layer stack 58. This defines conductivelines 72 (illustrated in FIGS. 12A through 13C) from the second materiallayers 54 in embodiments in which the second material layers 54 includeconductive materials. The conductive lines 72 may correspond to wordlines in the memory array 200 and the conductive lines 72 may providegate electrodes for the resulting transistors 204 of the memory array200. In FIGS. 11A through 19C, figures ending in “A” illustrate atop-down view, figures ending in “B” illustrate a cross-sectional viewalong line A-A′ of FIG. 1A, and figures ending in “C” illustrate across-sectional view along line B-B′ of FIG. 1A.

In FIGS. 11A through 11C a hard mask 80 is deposited over themulti-layer stack 58 and the IMD 70. The hard mask 80 may include, forexample, silicon nitride, silicon oxynitride, or the like, which may bedeposited by CVD, PVD, ALD, PECVD, or the like. The hard mask 80 can beformed by using a spin-on technique and can be patterned usingacceptable photolithography techniques. A patterned photoresist 82 isformed over the hard mask 80. The patterned photoresist 82 may be formedby depositing a photosensitive layer over the hard mask 80 using spin-oncoating or the like. The photosensitive layer may then be patterned byexposing the photosensitive layer to a patterned energy source (e.g., apatterned light source) and developing the photosensitive layer toremove an exposed or unexposed portion of the photosensitive layer,thereby forming the patterned photoresist 82. Trenches 86, which exposethe hard mask 80, are formed extending through the patterned photoresist82. The pattern of the patterned photoresist 82 corresponds toconductive lines to be formed in the multi-layer stack 58, as will bediscussed below with respect to FIGS. 12A through 12C.

In FIGS. 12A through 12C, the hard mask 80 is patterned using thepatterned photoresist 82 as a mask to extend the trenches 86 through thehard mask 80. The hard mask 80 may be patterned using an acceptableetching process, such as wet or dry etching, RIE, NBE, the like, or acombination thereof. The etching may be anisotropic. Thus, the trenches86 are extended through the hard mask 80 and expose the multi-layerstack 58. The patterned photoresist 82 may then be removed by anacceptable process, such as a wet etching process, a dry etchingprocess, a combination thereof, or the like.

In FIGS. 13A through 13C, the multi-layer stack 58 is patterned usingthe hard mask 80 as a mask to extend the trenches 86 through themulti-layer stack 58, exposing the substrate 50. The multi-layer stack58 may be patterned using one or more acceptable etching processes, suchas wet or dry etching, RIE, NBE, the like, or a combination thereof. Theetching processes may be anisotropic. Thus, the trenches 86 are extendedthrough the multi-layer stack 58. Etching the second material layers54A-54C forms conductive lines 72A-72C (e.g., word lines, collectivelyreferred to as conductive lines 72) from each respective layer of thesecond material layers 54. The trenches 86 separate adjacent conductivelines 72 and portions of the first material layers 52 from one another.Further in FIGS. 13A through 13C, the hard mask 80 may be removed by anacceptable process, such as a wet etching process, a dry etchingprocess, a planarization process, combinations thereof, or the like.

FIGS. 14A through 17C illustrate forming and patterning channel regionsfor the transistors 204 (see FIGS. 1A and 1B) in the trenches 86. InFIGS. 14A through 14C, a memory film 90 and an OS layer 92 are depositedin the trenches 86. The memory film 90 may be deposited conformally inthe trenches 86 along sidewalls of the conductive lines 72, the firstmaterial layers 52, and the IMD 70 and along top surfaces of the firstmaterial layer 52D and the IMD 70. The memory film 90 may be depositedby CVD, PVD, ALD, PECVD, or the like.

The memory film 90 may provide gate dielectrics for the transistors 204formed in the memory array 200. The memory film 90 may comprise amaterial that is capable of switching between two different polarizationdirections by applying an appropriate voltage differential across thememory film 90. The memory film 90 may be a high-k dielectric material,such as a hafnium (Hf) based dielectric material or the like. In someembodiments, the memory film 90 comprises a ferroelectric (FE) material,such as hafnium oxide, hafnium zirconium oxide, silicon-doped hafniumoxide, or the like. In some embodiments, the memory film 90 may comprisedifferent ferroelectric materials or different types of memorymaterials. In some embodiments, the memory film 90 may be a multilayermemory structure comprising a layer of SiN_(x), between two SiO_(x),layers (e.g., an ONO structure).

The OS layer 92 is conformally deposited in the trenches 86 over thememory film 90. The OS layer 92 comprises materials suitable forproviding channel regions for the transistors 204 (see FIGS. 1A and 1B).For example, the OS layer 92 may include zinc oxide (ZnO), indiumtungsten oxide (InWO), indium gallium zinc oxide (InGaZnO, IGZO), indiumzinc oxide (InZnO), indium tin oxide (ITO), polycrystalline silicon(poly-Si), silicon (Si), amorphous silicon (a-Si), combinations thereof,or the like. The OS layer 92 may be deposited by CVD, PVD, ALD, PECVD,or the like. The OS layer 92 may extend along sidewalls and bottomsurfaces of the trenches 86 over the memory film 90.

In FIGS. 15A through 15C, the OS layer 92 is etched using a suitableetch process, such as an anisotropic etch process, which separates theOS layer 92 into a plurality of OS layers 92. Horizontal portions of theOS layer 92, such as portions of the OS layer 92 extending along topsurfaces of the memory film 90, may be removed, while vertical portionsof the OS layer 92, such as portions of the OS layer 92 extending alongside surfaces of the memory film 90, remain. The suitable etch processmay be any acceptable etch process, such as wet or dry etching, RIE,NBE, the like, or a combination thereof.

In FIGS. 16A through 16C, the memory film 90 is etched using a suitableetch process, such as an anisotropic etch process, which separates thememory film 90 into a plurality of memory films 90. Horizontal portionsof the memory film 90, such as portions of the memory film 90 extendingalong top surfaces of the substrate 50 and the first material layer 52D,may be removed, while vertical portions of the memory film 90, such asportions of the memory film 90 extending along side surfaces of theconductive lines 72, the first material layers 52, and the IMD 70,remain. The suitable etch process may be any acceptable etch process,such as wet or dry etching, RIE, NBE, the like, or a combinationthereof. The OS layers 92 may mask portions of the memory film 90 duringthe etch process, such that the memory films 90 are L-shaped followingthe etch process.

In FIGS. 17A through 17C, dielectric materials 98 are deposited to fillremaining portions of the trenches 86. The dielectric materials 98 mayinclude, for example, silicon oxide, silicon nitride, siliconoxynitride, or the like, which may be deposited by CVD, PVD, ALD, PECVD,or the like. A removal process is applied to the dielectric materials98, the OS layers 92, and the memory films 90 to remove excess materialsover the conductive lines 72, the first material layers 52, and the IMD70. In some embodiments, a planarization process such as a CMP, anetch-back process, combinations thereof, or the like may be utilized.The planarization process exposes top surfaces of the IMD 70 and thefirst material layer 52D such that top surfaces of the first materiallayer 52D, the IMD 70, the memory films 90, the OS layers 92, and thedielectric materials 98 are level with one another after theplanarization process is complete.

FIGS. 18A through 21D illustrate intermediate steps of manufacturingdielectric materials 102, conductive lines 106 (e.g., bit lines), andconductive lines 108 (e.g., source lines) in the memory array 200. Theconductive lines 106 and the conductive lines 108 may extend in adirection perpendicular to the conductive lines 72 such that individualmemory cells 202 of the memory array 200 may be selected for read andwrite operations.

In FIGS. 18A through 18C, trenches 100 are patterned through thedielectric materials 98 and the OS layers 92. The trenches 100 may bepatterned in the dielectric materials 98 and the OS layers 92 through acombination of photolithography and etching. The etching may be anyacceptable etching processes, such as wet or dry etching, RIE, NBE, thelike, or a combination thereof. The etching may be anisotropic. Thetrenches 100 may be disposed between opposing sidewalls of the memoryfilms 90 and the trenches 100 may physically separate adjacent stacks ofthe memory cells 202 in the memory array 200 (see FIG. 1A). Thedielectric materials 98 and the OS layers 92 may be completely removedin the region 60, the region 62, and the region 64 of the staircasestructure 68 adjacent the IMD 70, the conductive lines 72, and the firstmaterial layers 52. In some embodiments (not separately illustrated),the trenches 100 may also be patterned through the memory films 90. Assuch, the trenches 100 may be disposed between opposing sidewalls of theconductive lines 72 and the first material layers 52 and the trenches100 may physically separate adjacent stacks of the memory cells 202 inthe memory array 200 (see FIG. 1A).

In FIGS. 19A through 19C, dielectric materials 102 are deposited in andfill the trenches 100. The dielectric materials 102 may include, forexample, silicon oxide, silicon nitride, silicon oxynitride, or thelike, which may be deposited by CVD, PVD, ALD, PECVD, or the like. Thedielectric materials 102 may extend along sidewalls and bottom surfacesof the trenches 100 over the memory films 90. After deposition, aplanarization process (e.g., a CMP, an etch-back, or the like) may beperformed to remove excess portions of the dielectric materials 102. Inthe resulting structure, top surfaces of the first material layer 52D,the memory films 90, the memory films 90, the IMD 70, the dielectricmaterials 98, and the dielectric materials 102 may be substantiallylevel (e.g., within process variations) with one another.

In some embodiments, materials of the dielectric materials 98 and thedielectric materials 102 may be selected so that they may be etchedselectively relative each other. For example, in some embodiments, thedielectric materials 98 are an oxide and the dielectric materials 102are a nitride. In some embodiments, the dielectric materials 98 are anitride and the dielectric materials 102 are an oxide. Other materialsare also possible.

FIG. 20A illustrates reference cross-sections of the memory array 200that are used in later figures. Cross-section A-A′ is along longitudinalaxes of conductive lines 72 and in a direction, for example, parallel tothe direction of current flow across the OS layers 92 of the transistors204. Cross-section B-B′ is perpendicular to the cross-section A-A′ andthe longitudinal axes of the conductive lines 72. The cross-section B-B′extends through the dielectric materials 98 and the dielectric materials102. Cross-section C-C′ is parallel to the cross-section B-B′ andextends through subsequently formed conductive lines (such as theconductive lines 106, discussed below with respect to FIGS. 21A through21D). Subsequent figures refer to these reference cross-sections forclarity. In FIGS. 20A through 21D, figures ending in “A” illustrate atop-down view, figures ending in “B” illustrate a cross-sectional viewalong line A-A′ of FIG. 20A, figures ending in “C” illustrate across-sectional view along line B-B′ of FIG. 20A, and figures ending in“D” illustrate a cross-sectional view along line C-C′ of FIG. 20A.

In FIGS. 20A through 20D, trenches 104 are patterned through thedielectric materials 98. The trenches 104 may be subsequently used toform conductive lines. The trenches 104 may be patterned through thedielectric materials 98 using a combination of photolithography andetching. The etching may be any acceptable etch process, such as wet ordry etching, RIE, NBE, the like, or a combination thereof. The etchingmay be anisotropic. The etching may use etchants that etch thedielectric materials 98 without significantly etching the dielectricmaterials 102, the OS layers 92, or the memory films 90. A pattern ofthe trenches 104 may correspond to that of subsequently formedconductive lines (such as the conductive lines 106 and the conductivelines 108, discussed below with respect to FIGS. 21A through 21D).Portions of the dielectric materials 98 may remain between each pair ofthe trenches 104, and the dielectric materials 102 may be disposedbetween adjacent pairs of the trenches 104. Further, portions of the OSlayers 92 and the memory films 90 may remain adjacent the trenches 104between the trenches 104 and each of the first material layers 52 andthe conductive lines 72. The portions of the OS layers 92 and the memoryfilms 90 may be used as part of subsequently formed transistors 204. Insome embodiments, a different etching may be used to pattern thetrenches 104 as opposed to the process used to pattern the trenches 100in order to selectively etch the material of the dielectric materials 98with respect to the OS layers 92 and the memory films 90.

In FIGS. 21A through 21D, the trenches 104 are filled with a conductivematerial to form conductive lines 106 and conductive lines 108. Memorycells 202 and transistors 204 are formed, which each include aconductive line 106, a conductive line 108, a conductive line 72 aportion of the memory films 90, and a portion of the OS layers 92. Theconductive lines 106 and the conductive lines 108 may each compriseconductive materials such as copper, titanium, titanium nitride,tantalum, tantalum nitride, tungsten, ruthenium, aluminum, combinationsthereof, or the like. The conductive lines 106 and the conductive lines108 may be formed using, for example, CVD, ALD, PVD, PECVD, or the like.After the conductive materials are deposited, a planarization (e.g., aCMP, an etch-back, or the like) may be performed to remove excessportions of the conductive materials, thereby forming the conductivelines 106 and the conductive lines 108. In the resulting structure, topsurfaces of the first material layer 52D, the IMD 70, the memory films90, the OS layers 92, the dielectric materials 98, the dielectricmaterials 102, the conductive lines 106, and the conductive lines 108may be substantially level (e.g., within process variations) with oneanother.

The conductive lines 106 may correspond to bit lines in the memory array200 and the conductive lines 108 may correspond to source lines in thememory array 200. Further, the conductive lines 106 and the conductivelines 108 may provide source/drain electrodes for the transistors 204 inthe memory array 200. Although FIG. 21D illustrates a cross-sectionalview that only shows the conductive lines 106, a cross-sectional view ofthe conductive lines 108 may be similar.

Although the channel regions for the transistors 204, the conductivelines 106, and the conductive lines 108 have been discussed as beingformed after forming the staircase structure 68, in some embodiments,the staircase structure 68 may be formed after forming the channelregions for the transistors 204, the conductive lines 106, and theconductive lines 108. For example, the manufacturing steps illustratedin and described with respect to FIGS. 4 through 10 to form thestaircase structure 68 may be performed after the manufacturing stepsillustrated in and described with respect to FIGS. 11A through 21D. Thesame or similar processes may be used in staircase-first andstaircase-last embodiments.

FIG. 22A illustrates reference cross-sections of the memory array 200that are used in later figures. Cross-section A-A′ is along longitudinalaxes of conductive lines 72 and in a direction, for example, parallel tothe direction of current flow across the OS layers 92 of the transistors204. Cross-section D-D′ is perpendicular to the cross-section A-A′ andthe longitudinal axes of the conductive lines 72. The cross-section D-D′extends through the region 60 of the staircase structure 68. Subsequentfigures refer to these reference cross-sections for clarity. In FIGS.22A through 24C, figures ending in “A” illustrate a top-down view,figures ending in “B” illustrate a cross-sectional view along line A-A′of FIG. 22A, and figures ending in “C” illustrate a cross-sectional viewalong line D-D′ of FIG. 22A.

In FIGS. 22A through 22C, trenches 110 are formed in the IMD 70. Thetrenches 110 may subsequently be used to form conductive contacts. Morespecifically, the trenches 110 may be subsequently used to formconductive contacts extending to the conductive lines 72 (e.g., wordline contacts, gate contacts, or the like). As illustrated in FIGS. 22Athrough 22C, the trenches 110 may extend through the IMD 70 and mayexpose top surfaces of the conductive lines 72. The staircase shape ofthe conductive lines 72 provides surfaces on each of the conductivelines 72 to which the trenches 110 may extend. The trenches 110 may beformed using a combination of photolithography and etching. The etchingmay be any acceptable etch process, such as wet or dry etching, RIE,NBE, the like, or a combination thereof. The etching may be anisotropic.

In some embodiments, the trenches 110 in the IMD 70 may be formed by aprocess having high etch selectivity to materials of the IMD 70. Assuch, the trenches 110 in the IMD 70 may be formed without significantlyremoving materials of the conductive lines 72. In some embodiments,openings exposing each of the conductive lines 72A-72C may be formedsimultaneously. Because of variations in the thickness of the IMD 70overlying each of the conductive lines 72A-72C, the conductive lines 72Cmay be exposed to the etching for a longer duration than the conductivelines 72B, which are exposed to the etching for a longer duration thanthe conductive lines 72A and so forth, with the conductive lines 72Abeing exposed to the etching for the shortest duration. Exposure to theetching may cause some material loss, pitting, or other damage in theconductive lines 72 such that the conductive lines 72C are damaged to agreatest extent, the conductive lines 72B are damaged to a decreasingextent, and the conductive lines 72A are damaged to a least extent.Forming the trenches 110 through the IMD 70 and exposing each of theconductive lines 72A-72C saves costs and time associated with performingmultiple masking and etching steps. However, some of the trenches 110may not be sufficiently etched, such that some of the conductive lines72 are not exposed. As such, a test structure (such as the teststructure 120 discussed below with respect to FIGS. 24A through 24D) maybe formed over the memory array 200 in order to detect any faultyconnections to the conductive lines 72. This reduces device defects.

In FIGS. 23A through 23C, conductive contacts 112 are formed in thetrenches 110. The conductive contacts 112 extend through the IMD 70 toeach of the conductive lines 72 and may be electrically coupled to theconductive lines 72. In some embodiments, the conductive contacts 112may be referred to as word line contacts, gate contacts, or the like.The conductive contacts 112 may be formed by forming a liner (notseparately illustrated), such as a diffusion barrier layer, an adhesionlayer, or the like, and a conductive material in the trenches 110. Theliner may include titanium, titanium nitride, tantalum, tantalumnitride, or the like. The conductive material may be copper, a copperalloy, silver, gold, tungsten, cobalt, aluminum, nickel, or the like. Aplanarization process, such as a CMP, may be performed to remove excessmaterial from a surface of the IMD 70. The remaining liner andconductive material form the conductive contacts 112 in the trenches110. As illustrated in FIGS. 23B and 23C, the conductive contacts 112may extend to each of the conductive lines 72A-72C.

In FIGS. 24A through 24D, a first dielectric layer 114, conductivecontacts 116, a second dielectric layer 115, and conductive lines 118are formed over the structure of FIGS. 23A through 23C. The conductivecontacts 112, the conductive contacts 116, and the conductive lines 118collectively form a test structure 120. The first dielectric layer 114and the second dielectric layer 115 may comprise dielectric materials,such as low-k dielectric materials, extra low-k (ELK) dielectricmaterials, or the like. In some embodiments, the first dielectric layer114 and the second dielectric layer 115 may comprise insulatingmaterials, such as silicon oxide, silicon nitride, silicon oxynitride,combinations thereof, or the like. The first dielectric layer 114 andthe second dielectric layer 115 may be deposited using an appropriateprocess, such as, CVD, ALD, PVD, PECVD, or the like.

Trenches (not separately illustrated), which may be used to form theconductive contacts 116 and the conductive lines 118, are formed throughthe second dielectric layer 115 and the first dielectric layer 114. Thetrenches in the second dielectric layer 115 expose top surfaces of thefirst dielectric layer 114 and the trenches in the first dielectriclayer 114 expose top surfaces of the conductive contacts 112. Thetrenches may be formed using a combination of photolithography andetching. The etching may be any acceptable etch process, such as wet ordry etching, RIE, NBE, the like, or a combination thereof. The etchingmay be anisotropic. The trenches in the second dielectric layer 115 andthe first dielectric layer 114 may be formed using multiple etchingprocesses.

The conductive contacts 116 and the conductive lines 118 are then formedin the trenches in the first dielectric layer 114 and the seconddielectric layer 115, respectively. The conductive contacts 116 and theconductive lines 118 may be formed by forming liners (not separatelyillustrated), such as diffusion barrier layers, adhesion layers, or thelike, and forming conductive materials over the liners. The conductivecontacts 116 and the conductive lines 118 may be formed simultaneously,or separately using one or more deposition processes. The liners mayinclude titanium, titanium nitride, tantalum, tantalum nitride, or thelike. The conductive materials may be copper, a copper alloy, silver,gold, tungsten, cobalt, aluminum, nickel, or the like. A planarizationprocess, such as a CMP, may be performed to remove excess material fromsurfaces of the second dielectric layer 115.

FIG. 24D illustrates a perspective view of the resulting structure,which includes the conductive lines 72, the conductive contacts 112, theconductive contacts 116, and the conductive lines 118, while otherstructures are omitted, in order to more clearly show relationshipsbetween the conductive lines 72, the conductive contacts 112, theconductive contacts 116, and the conductive lines 118. FIGS. 24A through24D further illustrate a conductive path through the test structure 120.The conductive path may extend from outside of a memory array 200 intothe memory array 200 at Point 1. The conductive path extends through aconductive line 118, a conductive contact 116, and a conductive contact112 to a conductive line 72A. The conductive path then extends throughthe conductive contacts 112, the conductive contacts 116, and aconductive line 118 through Points 2 and 3 to a conductive line 72B. Theconductive path continues through the memory array 200 to the Point 24,which extends outside the memory array 200. Each of the conductive lines72 is connected to a first vertically adjacent conductive line 72 andeither a second vertically adjacent conductive line 72 (e.g., aconductive line 72B is connected to a conductive line 72A and aconductive line 72C), a horizontally adjacent conductive line 72 (e.g.,a conductive line 72C is connected to a conductive line 72B and aconductive line 72C), or a connection outside of the memory array 200(e.g., a conductive line 72A is connected to a conductive line 72B andan outside connection). The conductive lines 118 include conductivelines 118 which extend in a direction parallel to longitudinal axes ofthe conductive lines 72, and which connect vertically adjacentconductive lines 72. The conductive lines 118 further include conductivelines 118 which extend in a direction perpendicular to the longitudinalaxes of the conductive lines 72, and which connect horizontally adjacentconductive lines 72, or which provide connections outside the memoryarray 200.

The test structure may be used to determine whether any connectionsbetween the conductive contacts 116 are faulty. For example, a voltagebias may be applied to the memory array 200 at Point 1 and Point 24.Because the conductive path extends through all of the conductive lines72, the conductive contacts 112, the conductive contacts 116, and theconductive lines 118 in the memory array 200, a current measurement maybe taken in order to determine whether any faulty connections arepresent. Thus, memory arrays 200 with faulty connections may bescreened, and device defects may be avoided. Additionally, as discussedabove, the trenches 110 and the conductive contacts 112 connected toeach of the conductive lines 72A-72C may be formed simultaneously, whichreduces costs, reduces manufacturing time, and increases devicethroughput.

FIGS. 25A through 25C illustrate scribe lines for separating variousmemory arrays 200. FIG. 25A illustrates a top-down view of four memoryarrays 200; FIG. 25B illustrates a perspective view of two memory arrays200; and FIG. 25C illustrates a top-down view of a wafer 300 including aplurality of memory arrays 200. The memory arrays 200 are laid out in agrid pattern in the wafer 300, which may be centered over the wafer 300.The scribe lines separate individual memory arrays 200, which will besubsequently diced by sawing along the scribe lines. As illustrated inFIGS. 25A and 25B, the scribe lines may extend through at least some ofthe conductive lines 118 (such as conductive lines 118 extending in thedirection perpendicular to longitudinal axes of the conductive lines 72)such that the conductive lines 118 are subsequently bisected. Asillustrated in FIG. 25C, the scribe lines may be disposed in areas 301between adjacent memory arrays 200, which areas 301 are removed by thedicing. At least portions of the test structures 120 may extend over theareas 301 and such portions of the test structures 120 may be removed bythe dicing. FIG. 25C further illustrates a defective memory array 200D,which may be detected through a respective test structure 120, andremoved. This reduces device defects.

FIGS. 26A through 34C illustrate an embodiment in which both the secondmaterial layers 54 comprise sacrificial materials, which are replaced byconductive materials. In FIGS. 26A through 34C, figures ending in “A”illustrate a cross-sectional view along line B-B′ of FIG. 1A, figuresending in “B” illustrate a cross-sectional view along line D-D′ of FIG.1A, and figures ending in “C” illustrate a cross-sectional view alongline C-C′ of FIG. 1A.

FIGS. 26A and 26B illustrate the multi-layer stack 58 after stepssimilar to or the same as those illustrated in FIGS. 3 through 10 anddiscussed above have been performed to form the staircase structure 68and the IMD 70 over the staircase structure 68. The multi-layer stack 58includes alternating layers of first material layers 52A-52D(collectively referred to as first material layers 52) and secondmaterial layers 54A-54C (collectively referred to as second materiallayers 54). The second material layers 54 may be replaced withconductive materials in subsequent steps to define conductive lines 422(e.g., word lines, illustrated in FIGS. 33A through 34C). The secondmaterial layers 54 may comprise insulating materials, such as siliconoxide, silicon nitride, silicon oxynitride, combinations thereof, or thelike. The first material layers 52 may comprise insulating materials,such as silicon oxide, silicon nitride, silicon oxynitride, combinationsthereof, or the like. The first material layers 52 may be formed of amaterial having high etch selectivity from the etching of the secondmaterial layers 54 and the substrate 50 may be formed of a materialhaving high etch selectivity from the etching of both the secondmaterial layers 54 and the first material layers 52 in order to aid withsubsequent etching steps. In some embodiments, the substrate 50 may beformed of silicon carbide, the first material layers 52 may be formed ofan oxide, such as silicon oxide, and the second material layers 54 maybe formed of a nitride, such as silicon nitride. The second materiallayers 54 and the first material layers 52 may each be formed using, forexample, CVD, ALD, physical vapor deposition (PVD), plasma enhanced CVD(PECVD), or the like. Although FIGS. 26A and 26B illustrate a particularnumber of the second material layers 54 and the first material layers52, other embodiments may include different numbers of the secondmaterial layers 54 and the first material layers 52.

Further in FIGS. 26A and 26B, a first patterned photoresist 400 isformed over the multi-layer stack 58 and first trenches 402 are formedextending through the multi-layer stack 58. The first patternedphotoresist 400 may be formed by depositing a photosensitive layer overthe first material layer 52D using spin-on coating or the like. Thephotosensitive layer may then be patterned by exposing thephotosensitive layer to a patterned energy source (e.g., a patternedlight source) and developing the photosensitive layer to remove anexposed or unexposed portion of the photosensitive layer, therebyforming the first patterned photoresist 400.

In the illustrated embodiment, the first trenches 402 extend through themulti-layer stack 58 to expose the substrate 50. In some embodiments,the first trenches 402 extend through some but not all layers of themulti-layer stack 58. The first trenches 402 may be formed usingacceptable photolithography and etching techniques, such as with anetching process that is selective to the multi-layer stack 58 (e.g.,etches the materials of the first material layers 52 and the secondmaterial layers 54 at a faster rate than the material of the substrate50). The etching may be any acceptable etch process, such as a reactiveion etch (RIE), neutral beam etch (NBE), the like, or a combinationthereof. The etching may be anisotropic. In embodiments in which thesubstrate 50 is formed of silicon carbide, the first material layers 52are formed of silicon oxide, and the second material layers 54 areformed of silicon nitride, the first trenches 402 may be formed by a dryetch using a fluorine-based gas (e.g., C₄F₆) mixed with hydrogen (H₂) oroxygen (O₂) gas.

In FIGS. 27A and 27B, the first trenches 402 are expanded to form firstsidewall recesses 404. Specifically, portions of the sidewalls of thesecond material layers 54 exposed by the first trenches 402 are recessedto form the first sidewall recesses 404. Although sidewalls of thesecond material layers 54 are illustrated as being straight, thesidewalls may be concave or convex. The first sidewall recesses 404 maybe formed by an acceptable etching process, such as one that isselective to the material of the second material layers 54 (e.g.,selectively etches the material of the second material layers 54 at afaster rate than the materials of the first material layers 52 and thesubstrate 50). The etching may be isotropic. In embodiments where thesubstrate 50 is formed of silicon carbide, the first material layers 52are formed of silicon oxide, and the second material layers 54 areformed of silicon nitride, the first trenches 402 can be expanded by awet etch using phosphoric acid (H₃PO₄). However, any suitable etchingprocess, such as a dry selective etch, may also be utilized. The firstpatterned photoresist 400 may be removed by an acceptable ashing or wetstrip process before or after forming the first sidewall recesses 404.

In FIGS. 28A and 28B, a conductive material 406 and a sacrificialmaterial 408 are formed in the first sidewall recesses 404 and to filland/or overfill the first trenches 402. One or more additional layers,such as seed layers, glue layers, barrier layers, diffusion layers, filllayers, and the like may also be filled in the first trenches 402 andthe first sidewall recesses 404. In some embodiments, the sacrificialmaterial 408 may be omitted. In embodiments which include a seed layer,the seed layer may comprise titanium nitride, tantalum nitride,titanium, tantalum, molybdenum, ruthenium, rhodium, hafnium, iridium,niobium, rhenium, tungsten, combinations of these, oxides of these, orthe like. The conductive material 406 may be formed of a conductivematerial, which may be a metal, such as tungsten, cobalt, aluminum,nickel, copper, silver, gold, molybdenum, ruthenium, molybdenum nitride,alloys thereof, or the like. In embodiments in which the first materiallayers 52 are formed of an oxide such as silicon oxide, the seed layercan be formed of titanium nitride and the conductive material 406 can beformed of tungsten. The sacrificial material 408 may comprise insulatingmaterials, such as silicon oxide, silicon nitride, silicon oxynitride,combinations thereof, or the like. The sacrificial material 408 mayinclude materials having a high etch selectivity to materials of thefirst material layers 52, the conductive material 406, and the substrate50 such that the sacrificial material 408 may be subsequently removedwithout removing or damaging the first material layers 52, theconductive material 406, or the substrate 50. The conductive material406 and the sacrificial material 408 may each be formed by an acceptabledeposition process such as chemical vapor deposition (CVD), atomic layerdeposition (ALD), physical vapor deposition (PVD), or the like.

Once the conductive material 406 and the sacrificial material 408 havebeen deposited in order to fill and/or overfill the first trenches 402,the conductive material 406 and the sacrificial material 408 may beplanarized to removed excess material outside of the first trenches 402,such that after the planarizing the conductive material 406 and thesacrificial material 408 completely span a top portion of the firsttrenches 402. In an embodiment, the conductive material 406 and thesacrificial material 408 may be planarized using, for example, achemical mechanical planarization (CMP) process. However, any suitableplanarization process, such as a grinding process, may also be utilized.

In FIGS. 29A and 29B, a second patterned photoresist 410 is formed overthe multi-layer stack 58 and second trenches 412 are formed extendingthrough the multi-layer stack 58. The second patterned photoresist 410may be formed by depositing a photosensitive layer over the firstmaterial layer 52D using spin-on coating or the like. The photosensitivelayer may then be patterned by exposing the photosensitive layer to apatterned energy source (e.g., a patterned light source) and developingthe photosensitive layer to remove an exposed or unexposed portion ofthe photosensitive layer, thereby forming the second patternedphotoresist 410.

In the illustrated embodiment, the second trenches 412 extend throughthe multi-layer stack 58 to expose the substrate 50. In someembodiments, the second trenches 412 extend through some but not alllayers of the multi-layer stack 58. The second trenches 412 may beformed using acceptable photolithography and etching techniques, such aswith an etching process that is selective to the multi-layer stack 58(e.g., etches the materials of the first material layers 52 and thesecond material layers 54 at a faster rate than the material of thesubstrate 50). The etching may be any acceptable etch process, such as aRIE, NBE, the like, or a combination thereof. The etching may beanisotropic. In embodiments in which the substrate 50 is formed ofsilicon carbide, the first material layers 52 are formed of siliconoxide, and the second material layers 54 are formed of silicon nitride,the second trenches 412 may be formed by a dry etch using afluorine-based gas (e.g., C₄F₆) mixed with hydrogen (H₂) or oxygen (O₂)gas.

In FIGS. 30A and 30B, the second trenches 412 are expanded to formsecond sidewall recesses 414. Specifically, the remaining portions ofthe second material layers 54 are removed to form the second sidewallrecesses 414. The second sidewall recesses 414 thus expose portions ofthe conductive material 406. The second sidewall recesses 414 may beformed by an acceptable etching process, such as one that is selectiveto the material of the second material layers 54 (e.g., selectivelyetches the material of the second material layers 54 at a faster ratethan the materials of the first material layers 52 and the substrate50). The etching may be any acceptable etch process, and in someembodiments, may be similar to the etch used to form the first sidewallrecesses 404 discussed with respect to FIGS. 27A and 27B. The secondpatterned photoresist 410 may be removed by an acceptable ashing or wetstrip process before or after forming the second sidewall recesses 414.

In FIGS. 31A and 31B, a conductive material 416 and a sacrificialmaterial 418 are formed in the second sidewall recesses 414 and to filland/or overfill the second trenches 412. One or more additional layers,such as seed layers, glue layers, barrier layers, diffusion layers, filllayers, and the like may also be filled in the second trenches 412 andthe second sidewall recesses 414. In some embodiments, the sacrificialmaterial 418 may be omitted. In embodiments which include a seed layer,the seed layer may comprise titanium nitride, tantalum nitride,titanium, tantalum, molybdenum, ruthenium, rhodium, hafnium, iridium,niobium, rhenium, tungsten, combinations of these, oxides of these, orthe like. The conductive material 416 may be formed of a conductivematerial, which may be a metal, such as tungsten, cobalt, aluminum,nickel, copper, silver, gold, molybdenum, ruthenium, molybdenum nitride,alloys thereof, or the like. In embodiments in which the first materiallayers 52 are formed of an oxide such as silicon oxide, the seed layercan be formed of titanium nitride and the conductive material 416 can beformed of tungsten. The sacrificial material 418 may comprise insulatingmaterials, such as silicon oxide, silicon nitride, silicon oxynitride,combinations thereof, or the like. The sacrificial material 418 mayinclude materials having a high etch selectivity to materials of thefirst material layers 52, the conductive material 416, and the substrate50 such that the sacrificial material 418 may be subsequently removedwithout removing or damaging the first material layers 52, theconductive material 416, or the substrate 50. The conductive material416 and the sacrificial material 418 may each be formed by an acceptabledeposition process such as CVD, ALD, PVD, or the like.

Once the conductive material 416 and the sacrificial material 418 havebeen deposited in order to fill and/or overfill the second trenches 412,the conductive material 416 and the sacrificial material 418 may beplanarized to removed excess material outside of the second trenches412, such that after the planarizing the conductive material 416 and thesacrificial material 418 completely span a top portion of the secondtrenches 412. In an embodiment, the conductive material 416 and thesacrificial material 418 may be planarized using, for example, a CMPprocess. However, any suitable planarization process, such as a grindingprocess, may also be utilized.

In FIGS. 32A and 32B, the sacrificial materials 408 and 418 may beremoved by an acceptable process forming third trenches 420. Theacceptable process may be a wet etching process, a dry etching process,a combination thereof, or the like. In some embodiments, the sacrificialmaterials 408 and 418 may be removed by an isotropic etching process,which is selective to the materials of the sacrificial materials 408 and418. As such, the sacrificial materials 408 and 418 may be removedwithout removing or damaging the first material layers 52, theconductive material 406, the conductive material 416, or the substrate50.

In FIGS. 33A and 33B, the conductive materials 406 and 416 are etched toexpand the third trenches 420 and form conductive lines 422A-422C (e.g.,word lines, collectively referred to as conductive lines 422) from eachrespective layer of the conductive materials 406 and 416. The thirdtrenches 420 separate adjacent conductive lines 422 and portions of thefirst material layers 52 from one another. Because the conductive lines422 are formed from adjacent portions of the conductive materials 406and 416, each of the conductive lines 422 may comprise a seam, asillustrated in FIGS. 33A and 33B. Etching the conductive materials 406and 416 to expand the third trenches 420 may expose sidewalls of thefirst material layers 52. In some embodiments, the conductive materials406 and 416 may be etched using, for example, an anisotropic etchingprocess However, any suitable etching process may be utilized. In someembodiments, the etching process is performed until the material of theconductive materials 406 and 416 that extends beyond sidewalls of thefirst material layers 52 has been removed and sidewalls of theconductive materials 406 and 416 are flush with sidewalls of the firstmaterial layers 52. As such, the conductive lines 422 may have widthssimilar to or the same as the first material layers 52. Althoughsidewalls of the conductive lines 422 are illustrated as being straight,the sidewalls may be concave or convex.

Forming the conductive lines 422 by forming and replacing the secondmaterial layers 54 in the multi-layer stack 58 improves the aspect ratioof columns of the memory array 200, and prevents twisting or collapsingof features during formation. This reduces device defects and improvesdevice performance. The steps performed in FIGS. 26A through 33B may beperformed in place of the steps performed in FIGS. 11A through 13C, withthe remaining steps for forming the memory array 200 being the same asthose discussed above (e.g., the steps performed in FIGS. 3 through 10are performed, then the steps performed in FIGS. 26A through 33B areperformed, and finally, the steps performed in FIGS. 14B through 24D areperformed.

FIGS. 34A through 34C illustrate the embodiment of FIGS. 26A through 33Bafter the steps of FIGS. 14B through 24D are performed. The structuresof FIG. 34B may be similar to those illustrated in FIG. 24C, except thatthe conductive lines 72 are replaced by the conductive lines 422 formedfrom the conductive materials 406 and 416.

Embodiments may achieve various advantages. For example, forming thetrenches 110 extending to the conductive lines 72A-72C simultaneouslyand forming the conductive contacts 112 in the trenches 110simultaneously reduces production time, reduces costs associated withadditional patterning process, and increases throughput. The teststructures 120 may be formed over the memory arrays 200 in order tocheck for faulty connections. As such, defective memory arrays 200 maybe removed and device defects may be reduced.

In accordance with an embodiment, a memory array includes a first wordline over a semiconductor substrate, a longitudinal axis of the firstword line extending in a first direction; a second word line over thefirst word line in a second direction perpendicular to a major surfaceof the semiconductor substrate, a longitudinal axis of the second wordline extending in the first direction; a memory film contacting thefirst word line and the second word line; an oxide semiconductor (OS)layer contacting a first source line and a first bit line, the memoryfilm being between the OS layer and each of the first word line and thesecond word line; and a test structure over the first word line and thesecond word line, the test structure including a first conductive lineelectrically coupling the first word line to the second word line, alongitudinal axis of the first conductive line extending in the firstdirection. In an embodiment, the first word line has a first lengthgreater than a second length of the second word line. In an embodiment,the test structure further includes a second conductive line, the secondconductive line is electrically coupled to the first word line, thesecond conductive line extends to a boundary of the memory array, and alongitudinal axis of the second conductive line extends in the firstdirection. In an embodiment, the memory array further includes a thirdword line adjacent the first word line in a third directionperpendicular to the first direction, the memory film and the OS layerbeing between the first word line and the third word line in the thirddirection, the test structure further includes a second conductive line,the second conductive line electrically coupling the first word line tothe third word line, and a longitudinal axis of the second conductiveline extending in the third direction. In an embodiment, the first wordline includes a seam between a first conductive material and a secondconductive material. In an embodiment, the memory array further includesa third word line below the first word line in the second direction, alongitudinal axis of the third word line extending in the firstdirection, the test structure further includes a second conductive lineelectrically coupling the first word line to the third word line, alongitudinal axis of the second conductive line extending in the firstdirection. In an embodiment, the first word line has a first lengthgreater than a second length of the second word line, and the third wordline has a third length greater than the first length.

In accordance with another embodiment, a device includes a first wordline over a semiconductor substrate, the first word line having a firstlength in a first direction; a second word line over the semiconductorsubstrate, the second word line having a second length in the firstdirection, the second length being equal to the first length; a firstinter-metal dielectric (IMD) over the first word line; a first memoryfilm in contact with the first word line and the first IMD; a firstoxide semiconductor (OS) layer over the first memory film, the first OSlayer contacting a source line and a bit line; a first conductivecontact extending through the first IMD and electrically coupled to thefirst word line; a second conductive contact electrically coupled to thesecond word line; and a first conductive line extending over the firstIMD and electrically coupling the first conductive contact to the secondconductive contact, the first conductive line extending in a seconddirection perpendicular to the first direction. In an embodiment, afirst distance between the first word line and the semiconductorsubstrate in a third direction perpendicular to a major surface of thesemiconductor substrate is equal to a second distance between the secondword line and the semiconductor substrate in the third direction. In anembodiment, the IMD has a staircase structure in a cross-sectional view.In an embodiment, the device further includes a second memory film incontact with the second word line; a second OS layer over the secondmemory film, the second OS layer contacting the source line and the bitline; and a first dielectric material separating the first OS layer fromthe second OS layer. In an embodiment, the device further includes asecond IMD over the second word line, the second memory film being incontact with the second IMD; and a second dielectric material separatingthe first IMD from the second IMD, the second dielectric materialincluding a different material from the first dielectric material. In anembodiment, the device further includes a third word line over thesemiconductor substrate, the third word line having a third length inthe first direction, the third length being different from the firstlength and the second length; a third conductive contact electricallycoupled to the first word line; a fourth conductive contact electricallycoupled to the third word line; and a second conductive lineelectrically coupling the third conductive contact to the fourthconductive contact, the second conductive line extending in the firstdirection. In an embodiment, the first OS layer is between the firstconductive contact and the third conductive contact in the firstdirection.

In accordance with yet another embodiment, a method includes depositinga multi-layer stack over a semiconductor substrate, the multi-layerstack including alternating layers of a first material and a secondmaterial; patterning the multi-layer stack such that the multi-layerstack includes a staircase structure in a cross-sectional view; formingan inter-metal dielectric (IMD) over the staircase structure of themulti-layer stack; forming a plurality of word lines in the multi-layerstack; depositing a memory film in the multi-layer stack adjacent theplurality of word lines; depositing an oxide semiconductor (OS) layerover the memory film; etching the IMD to form a first opening exposing afirst word line of the plurality of word lines and a second openingexposing a second word line of the plurality of word lines, the firstopening extending to a first depth, and the second opening extending toa second depth different from the first depth; forming a firstconductive contact in the first opening and electrically coupled to thefirst word line and a second conductive contact in the second openingand electrically coupled to the second word line; and forming a firstconductive line over the IMD, the first conductive contact, and thesecond conductive contact, the first conductive line electricallycoupling the first conductive contact to the second conductive contact.In an embodiment, the first conductive line, the first word line, andthe second word line extend in a first direction. In an embodiment, themethod further includes etching the IMD to form a third opening exposingthe first word line and a fourth opening exposing a third word line ofthe plurality of word lines, the third opening and the fourth openingextending to the first depth; forming a third conductive contact in thethird opening and electrically coupled to the first word line and afourth conductive contact in the fourth opening and electrically coupledto the third word line; and forming a second conductive line over theIMD, the third conductive contact, and the fourth conductive contact,the second conductive line electrically coupling the third conductivecontact to the fourth conductive contact. In an embodiment, the firstword line and the second word line extend in a first direction, and thesecond conductive line extends in a second direction perpendicular tothe first direction. In an embodiment, the first material includes adielectric material, the second material includes a conductive material,and forming the plurality of word lines in the multi-layer stackincludes patterning the multi-layer stack to separate adjacent wordlines formed of the second material. In an embodiment, the firstmaterial includes an oxide, the second material includes a nitride,forming the plurality of word lines in the multi-layer stack includespatterning the multi-layer stack and replacing the second material witha conductive material.

One general aspect of embodiments disclosed herein includes a first wordline over a semiconductor substrate, the first word line having a firstlength in a first direction. The device also includes a second word lineover the semiconductor substrate, the second word line having a secondlength in the first direction, where the second length is equal to thefirst length. The device also includes a first inter-metal dielectric(IMD) over the first word line. The device also includes a first memoryfilm in contact with the first word line and the first IMD. The devicealso includes a first oxide semiconductor (OS) layer over the firstmemory film, the first OS layer contacting a source line and a bit line.The device also includes a first conductive contact extending throughthe first IMD and electrically coupled to the first word line. Thedevice also includes a second conductive contact electrically coupled tothe second word line. The device also includes and a first conductiveline extending over the first IMD and electrically coupling the firstconductive contact to the second conductive contact, where the firstconductive line extends in a second direction perpendicular to the firstdirection.

Another general aspect of embodiments disclosed herein includesdepositing a multi-layer stack over a semiconductor substrate, themulti-layer stack may include alternating layers of a first material anda second material. The method also includes patterning the multi-layerstack such that the multi-layer stack may include a staircase structurein a cross-sectional view. The method also includes forming aninter-metal dielectric (IMD) over the staircase structure of themulti-layer stack. The method also includes forming a plurality of wordlines in the multi-layer stack. The method also includes depositing amemory film in the multi-layer stack adjacent the plurality of wordlines. The method also includes depositing an oxide semiconductor (OS)layer over the memory film. The method also includes etching the IMD toform a first opening exposing a first word line of the plurality of wordlines and a second opening exposing a second word line of the pluralityof word lines, where the first opening extends to a first depth, andwhere the second opening extends to a second depth different from thefirst depth. The method also includes forming a first conductive contactin the first opening and electrically coupled to the first word line anda second conductive contact in the second opening and electricallycoupled to the second word line. The method also includes and forming afirst conductive line over the IMD, the first conductive contact, andthe second conductive contact, where the first conductive lineelectrically couples the first conductive contact to the secondconductive contact.

A further general aspect of embodiments disclosed herein includesmulti-layer stack over a semiconductor substrate, the multi-layer stackmay include alternating layers of a first material and a secondmaterial, a first layer of the multi-layer stack extending a firstlength in a first direction, each next layer in the multi-layer stack,preceding from a top of the multi-layer stack to a bottom of themulti-layer stack, extending a next length in the first direction, thenext length being greater than the length of the immediately precedinglayer of the multi-layer stack. The device also includes an inter-metaldielectric (IMD) over the multi-layer stack. The device also includes aplurality of word lines in the multi-layer stack. The device alsoincludes a memory film in the multi-layer stack adjacent the pluralityof word lines. The device also includes a first oxide semiconductor (OS)layer over the memory film. The device also includes a first conductivecontact extending to a first depth in the multi-layer stack andelectrically contacting a first word line. The device also includes asecond conductive contact extending a second depth into the multi-layerstack and electrically contacting a second word line. The device alsoincludes and a first conductive line over the IMD, the first conductivecontact, and the second conductive contact, where the first conductiveline electrically couples the first conductive contact to the secondconductive contact.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a first word line over asemiconductor substrate, the first word line having a first length in afirst direction; a second word line over the semiconductor substrate,the second word line having a second length in the first direction,wherein the second length is equal to the first length; a firstinter-metal dielectric (IMD) over the first word line; a first memoryfilm in contact with the first word line and the first IMD; a firstoxide semiconductor (OS) layer over the first memory film, the first OSlayer contacting a source line and a bit line; a first conductivecontact extending through the first IMD and electrically coupled to thefirst word line; a second conductive contact electrically coupled to thesecond word line; and a first conductive line extending over the firstIMD and electrically coupling the first conductive contact to the secondconductive contact, wherein the first conductive line extends in asecond direction perpendicular to the first direction.
 2. The device ofclaim 1, wherein a first distance between the first word line and thesemiconductor substrate in a third direction perpendicular to a majorsurface of the semiconductor substrate is equal to a second distancebetween the second word line and the semiconductor substrate in thethird direction.
 3. The device of claim 1, wherein the first IMD has astaircase structure in a cross-sectional view.
 4. The device of claim 1,further comprising: a second memory film in contact with the second wordline; a second OS layer over the second memory film, the second OS layercontacting the source line and the bit line; and a first dielectricmaterial separating the first OS layer from the second OS layer.
 5. Thedevice of claim 4, further comprising: a second IMD over the second wordline, wherein the second memory film is in contact with the second IMD;and a second dielectric material separating the first IMD from thesecond IMD, the second dielectric material comprising a differentmaterial from the first dielectric material.
 6. The device of claim 1,further comprising: a third word line over the semiconductor substrate,the third word line having a third length in the first direction,wherein the third length is different from the first length and thesecond length; a third conductive contact electrically coupled to thefirst word line; a fourth conductive contact electrically coupled to thethird word line; and a second conductive line electrically coupling thethird conductive contact to the fourth conductive contact, wherein thesecond conductive line extends in the first direction.
 7. The device ofclaim 6, wherein the first OS layer is between the first conductivecontact and the third conductive contact in the first direction.
 8. Amethod comprising: depositing a multi-layer stack over a semiconductorsubstrate, the multi-layer stack comprising alternating layers of afirst material and a second material; patterning the multi-layer stacksuch that the multi-layer stack comprises a staircase structure in across-sectional view; forming an inter-metal dielectric (IMD) over thestaircase structure of the multi-layer stack; forming a plurality ofword lines in the multi-layer stack; depositing a memory film in themulti-layer stack adjacent the plurality of word lines; depositing anoxide semiconductor (OS) layer over the memory film; etching the IMD toform a first opening exposing a first word line of the plurality of wordlines and a second opening exposing a second word line of the pluralityof word lines, wherein the first opening extends to a first depth, andwherein the second opening extends to a second depth different from thefirst depth; forming a first conductive contact in the first opening andelectrically coupled to the first word line and a second conductivecontact in the second opening and electrically coupled to the secondword line; and forming a first conductive line over the IMD, the firstconductive contact, and the second conductive contact, wherein the firstconductive line electrically couples the first conductive contact to thesecond conductive contact.
 9. The method of claim 8, wherein the firstconductive line, the first word line, and the second word line extend ina first direction.
 10. The method of claim 8, further comprising:etching the IMD to form a third opening exposing the first word line anda fourth opening exposing a third word line of the plurality of wordlines, wherein the third opening and the fourth opening extend to thefirst depth; forming a third conductive contact in the third opening andelectrically coupled to the first word line and a fourth conductivecontact in the fourth opening and electrically coupled to the third wordline; and forming a second conductive line over the IMD, the thirdconductive contact, and the fourth conductive contact, wherein thesecond conductive line electrically couples the third conductive contactto the fourth conductive contact.
 11. The method of claim 10, whereinthe first word line and the second word line extend in a firstdirection, and wherein the second conductive line extends in a seconddirection perpendicular to the first direction.
 12. The method of claim8, wherein the first material comprises a dielectric material, whereinthe second material comprises a conductive material, and wherein formingthe plurality of word lines in the multi-layer stack comprisespatterning the multi-layer stack to separate adjacent word lines formedof the second material.
 13. The method of claim 8, wherein the firstmaterial comprises an oxide, wherein the second material comprises anitride, wherein forming the plurality of word lines in the multi-layerstack comprises patterning the multi-layer stack and replacing thesecond material with a conductive material.
 14. A device comprising:multi-layer stack over a semiconductor substrate, the multi-layer stackcomprising alternating layers of a first material and a second material,a first layer of the multi-layer stack extending a first length in afirst direction, each next layer in the multi-layer stack, precedingfrom a top of the multi-layer stack to a bottom of the multi-layerstack, extending a next length in the first direction, the next lengthbeing greater than the length of the immediately preceding layer of themulti-layer stack; an inter-metal dielectric (IMD) over the multi-layerstack; a plurality of word lines in the multi-layer stack; a memory filmin the multi-layer stack adjacent the plurality of word lines; a firstoxide semiconductor (OS) layer over the memory film; a first conductivecontact extending to a first depth in the multi-layer stack andelectrically contacting a first word line; a second conductive contactextending a second depth into the multi-layer stack and electricallycontacting a second word line; and a first conductive line over the IMD,the first conductive contact, and the second conductive contact, whereinthe first conductive line electrically couples the first conductivecontact to the second conductive contact.
 15. The device of claim 14,further comprising: a third conductive contact extending a third depthinto the multi-layer stack and electrically contacting the first wordline and a fourth conductive contact extending the third depth into themulti-layer stack and electrically contacting a third word line; and asecond conductive line over the IMD, the third conductive contact, andthe fourth conductive contact, wherein the second conductive lineelectrically couples the third conductive contact to the fourthconductive contact.
 16. The device of claim 15, wherein the first wordline and the second word line extend in a first direction, and whereinthe second conductive line extends in a second direction perpendicularto the first direction.
 17. The device of claim 14, wherein the firstmaterial comprises a dielectric material, wherein the second materialcomprises a conductive material, and wherein the plurality of word linesin the multi-layer stack comprises the conductive material.
 18. Thedevice of claim 14, wherein a first distance between the first word lineand the semiconductor substrate in a direction perpendicular to a majorsurface of the semiconductor substrate is equal to a second distancebetween the second word line and the semiconductor substrate.
 19. Thedevice of claim 14, wherein the IMD has a staircase structure in across-sectional view.
 20. The device of claim 14, further comprising: asecond memory film in contact with the second word line; a second OSlayer over the second memory film; and a first dielectric materialseparating the first OS layer from the second OS layer.